Field of the Invention
The present invention relates to a method for polishing a semiconductor substrate such as a semiconductor wafer.
Background Art
Recently, the miniaturization of semiconductor devices has progressed with the high integration or the like of integrated circuits, and consequently, in addition to high flatness, a high level reduction of surface defects has been required for semiconductor substrates (hereinafter, also simply referred to as substrates) such as semiconductor wafers (hereinafter, also simply referred to as wafers).
For the purpose of making such semiconductor substrates more flat and reducing such surface defects, polishing of the surface of substrates with a polishing composition including a water-soluble polymer, which is a component enhancing the wettability to semiconductor substrates, has been considered. Such a polishing composition used in the method for polishing is described in, for example, Patent Literature 1. Patent Literature 1 describes a polishing composition including hydroxyethyl cellulose as a water-soluble polymer.
The polishing of a semiconductor substrate usually adopts polishing methods performing polishing as multiple stages. In a multi-stage polishing method, the surface of a semiconductor substrate is polished flat in an early stage polishing such as the polishing in a first stage, a second stage and the like, and in the final polishing, a polishing designed for the purpose of achieving a more precise flatness is performed.
In general, surface defects having various sizes are present in a mixed manner on the surface of semiconductor substrates before polishing; however, in order to perform a polishing designed for the purpose of achieving a highly precise flatness as described above in the final polishing, a polishing composition mainly reducing the surface defects having minute sizes is used. Such a conventional polishing composition as described in Patent Literature 1 cannot selectively remove surface defects having specific sizes; consequently, when such a polishing composition is used in the polishing in the stages earlier than the final polishing, the surface defects having relatively large sizes and the surface defects having relatively small sizes on a substrate are equally polished. Accordingly, there is a possibility that surface defects having relatively larger sizes remain. Thus, there is a problem that even when a final polishing is performed in such a state, the surface defects after the final polishing cannot be sufficiently reduced.